1. Field of the Invention
The invention relates to improvements in developing units which are typically positioned about a photoconductive element such as a photoconductive drum in an image forming apparatus such as a copier, facsimile machine, printer, etc.
2. Discussion of the Background
A conventional developing device for an image forming apparatus can be provided in the form of a unit having two developing rollers disposed such that each developing roller axis is supported by the housing or side plates of the unit. In this type of developing device, providing predetermined gaps between the photoconductive element, particularly a photoconductive drum, and each of the developing rollers is important in reliably obtaining a high quality copied image, and in avoiding excessive driving loads imposed upon the developing rollers during a developing operation. Of course, where only one developing roller is utilized in the developing unit, it is relatively easy to set the gap between the photoconductive drum and the developing roller. In particular, where the developing unit includes only a single developing roller, the developing unit need only ensure a predetermined gap is provided between the single developing roller and the photoconductive drum. However, where two or more developing rollers are used, and each is supported by the side plates or housing of the developing unit, it can be difficult to position the unit such that a predetermined gap is maintained between the photoconductive drum and each of the respective developing rollers. The problem of properly positioning each of the rollers with respect to the photoconductive drum can be particularly difficult as a result of errors which can occur upon setting or placing of the developing unit in the body of the image forming apparatus (such as a copying machine) and/or during assembly of the developing unit. For example, the axes of the developing rollers might not be consistent with respect to one another in the developing unit, and/or might not be consistently disposed at the exact location in the housing of the developing unit. In addition, during placement of the unit in the image forming apparatus, adjusting of the gap for one of the developing rollers can result in an improper gap setting for the other developing roller(s).
One type of conventional developing device for an image forming apparatus is disclosed in Japanese Laid Open Patent Publication No. 63-98674/88, which includes an arrangement to avoid the above-discussed problem. In this type of device, one of the developing rollers is positioned with a predetermined gap with respect to the photoconductive drum, and thereafter the unit (which includes two developing rollers) is rotated or pivoted around the axis of the first positioned roller in a predetermined direction. As a result, the other developing roller is positioned against the photoconductive drum. However, such a device requires a complicated setting action, and can incumber the design of the surrounding parts, or require a sufficient space to be accommodated with respect to the surrounding parts to accommodate the setting action. As a result, the developing device can become complicated and inefficient from a cost standpoint.